Radiation-sensitive compositions are routinely used in the preparation of imagable materials including lithographic printing plate precursors. Such compositions generally include a radiation-sensitive component, an initiator system, and a binder, each of which has been the focus of research to provide various improvements in physical properties, imaging performance, and image characteristics.
Recent developments in the field of printing plate precursors concern the use of radiation-sensitive compositions that can be imaged by means of lasers or laser diodes, and more particularly, that can be imaged and/or developed on-press. Laser exposure does not require conventional silver halide graphic arts films as intermediate information carriers (or “masks”) since the lasers can be controlled directly by computers. High-performance lasers or laser-diodes that are used in commercially-available image-setters generally emit radiation having a wavelength of at least 700 nm, and thus the radiation-sensitive compositions are required to be sensitive in the near-infrared or infrared region of the electromagnetic spectrum. However, other useful radiation-sensitive compositions are designed for imaging with ultraviolet or visible radiation.
There are two possible ways of using radiation-sensitive compositions for the preparation of printing plates. For negative-working printing plates, exposed regions in the radiation-sensitive compositions are hardened and unexposed regions are washed off during development. For positive-working printing plates, the exposed regions are dissolved in a developer and the unexposed regions become an image.
Various negative-working radiation compositions and imagable elements are described in and U.S. Pat. Nos. 6,309,792 (Hauck et al.), 6,569,603 (Furukawa), 6,893,797 (Munnelly et al.), 6,787,281 (Tao et al.), and 6,899,994 (Huang et al.), U.S. Patent Application Publications 2003/0118939 (West et al.), 2005/0008971 (Mitsumoto et al.), 2005/0204943 (Makino et al.), and 2007/0184380 (Tao et al.), and EP 1,079,276A (Lifka et al.), EP 1,182,033A (Fujimaki et al.), and EP 1,449,650A (Goto). Various negative-working imagable elements have been designed for processing or development “on-press” using a fountain solution, lithographic printing ink, or both, as described, for example, in U.S. Patent Application Publication 2005-263021 (Mitsumoto et al.) and in U.S. Pat. Nos. 6,071,675 (Teng), 6,387,595 (Teng), 6,482,571 (Teng), 6,495,310 (Teng), 6,541,183 (Teng), 6,548,222 (Teng), 6,576,401 (Teng), 6,902,866 (Teng), and 7,089,856 (Teng).
Various means for stabilizing imagable elements have been described in the literature and tried in commercial products. For example, U.S. Pat. No. 5,795,698 (Fitzgerald et al.) describes the use of amphoteric hydrogen bond-forming developability stabilizers in lithographic printing plate precursors. U.S. Pat. No. 7,175,969 (Ray et al.) describes an improvement of storage stability by enclosing the imagable elements inside of water-impermeable sheet materials. Specific polymeric binders are used to improve storage stability of on-press developable imagable elements in U.S. Pat. No. 7,172,850 (Munnelly et al.)